I tried installing FreeBSD 12.0 from a USB, which went fine except that I had to do it in safe mode. After that there were no issues with the installation process save for networking.
Now that FreeBSD is installed (and the USB is removed), the installation menu still pops up when I start the machine, i.e. this menu:
1. Boot Multi user 2. Boot Single user 3. Escape to loader prompt 4. Reboot Options: 5. Kernel: default/kernel (1 of 1) 6. Boot Options
Should I choose one of those, again, to get to a shell so that I can login? If so, which option? Looks more like something went horribly wrong.
FreeBSD is the only thing installed on the device (x86-64), and I have made no tweaks to the system (afaik).